The present invention relates to a serum separating device and an apparatus for serum separation which are used at the time of the separation of a blood sample into serum and clot by means of centrifugal separation and the like.
Conventionally, since diagnostic tests for blood samples are primarily conducted using serum (plasma), a preprocessing operation prior to testing is required in which a blood sample which is collected in a blood collection tube is separated into a serum or plasma (hereinafter referred to as serum) and a clot or blood cells (hereinafter referred to as a clot).
Commonly, in such a serum separation operation, the whole blood sample which is collected is placed in a blood collection tube, this is subjected to centrifugal separation, and the serum which comprises the sample is separated therefrom. However, in such centrifugal separators, the state of the separation of the serum and the clot is extremely unstable, and if the slightest shock is applied, the blood cells present in the clot which is sedimented contaminates the serum, so that extremely careful operations are required in the handling of the blood sample after separation.
Various devices have been proposed in order to improve this unstable separation state of the blood sample after centrifugal separation, and to simplify the testing operation; an example thereof is a method employing a sealant possessing thixotropic characteristics and having a specific gravity between that of serum and clot.
This sealant has, for example, a synthetic resin of low molecular weight such as silicone oil or the like as a primary component thereof, and possesses a stable specific gravity and thixotropic characteristics; during centrifugal separation, this sealant becomes liquid and forms a strong partition above the clot.
However, the following difficulties are present in this sealant.
(1) In the case in which the material in the clot is abnormal, it is impossible to form a strong partition. For example, in the case in which the specific gravity of the clot is small and the clot is soft, as is seen in dialysis patients, it is impossible to completely separate the serum from the clot. PA0 (2) Since the sealant is water insoluble, the sealant is mutually dissolvable with lipid-soluble drugs which are difficult to dissolve in water. Accordingly, in the case in which the drug concentration present in the blood is to be measured, there are cases in which the drugs dissolve in the sealant, and the values obtained by diagnostic tests are thus incorrect. PA0 (3) In the case in which blood coagulation factor is the object of test, the sealant activates the blood coagulation factor, so that it is impossible to employ such a sealant. PA0 (4) Blood properties vary from person to person. In particular, the generation of fibrin is a hindrance to the diagnostic test of serum after centrifugal separation, so that it is necessary to screen this fibrin which is thus generated; however, when a sealant is employed, it is impossible to screen this fibrin. Fibrin is particularly readily generated in the blood of dialysis patients, so that it is impossible to prevent the generation of fibrin when a sealant is employed.
The use of, for example, a serum filtering piston such as that shown in FIG. 9 is proposed to solve these difficulties with the use of the sealant (Japanese Patent Application, First Publication, Laid-Open No. Sho 51-105890).
This serum filtering piston 1 comprising a disc-shaped filter 2 with a diameter which slightly larger than the inner diameter of the blood collection tube, and a cylindrical weight 3 which attaches to the center of filter 2 and a diameter which smaller than that of filter 2; as shown in FIG. 10, after the collected blood 5 is placed in the blood collection tube 4, the serum filtering piston 1 is inserted into the blood collection tube 4, and by means of subsequently conducting centrifugal separation, as shown in FIG. 11, this serum filtering piston 1 moves to the boundary between serum 6 and clot 7, and since the filter 2 is in tight contact with the inner wall 4a of the blood collection tube 4, serum 6 and clot 7 are completely separated, and it is possible to obtain the serum by means of decanting.
An evacuated blood collection tube, in which a rubber stopper is inserted in an evacuated state into the mouth of a conventional blood collection tube, is employed as the vessel used in serum separation; however, recently, the use of an evacuated blood collection tube, in which a gas-barrier-type film such as aluminum laminate or the like is heat-sealed onto the mouth of a blood collection tube in an evacuated state, and a thin rubber flap is attached to the center of this film, has been proposed in order to increase air-tightness.
However, the serum filtering piston 1 described above has a construction in which the filter 2 is fastened to the weight 3 by a pin, so that there is some danger that the filter 2 will be torn off. Furthermore, in piston 1, filter 2 is drawn downward in a sliding manner, so that it is necessary that filter 2 possess a certain degree of strength, so that it bends and moves downward while sliding along the inner wall 4a of the blood collection tube 4. For this reason, the clot which adheres to the inner wall 4a is scraped, and this leads to blood cell breakage, so that as an effect thereof, inaccurate test values of LDH (lactic acid dehydrogenase) or the like occur. Furthermore, filter 2 moves easily from side to side, so that accordingly, it is difficult to continuously support the filter 2 horizontally in a balanced manner, and there are problems in that during the recovery of serum after centrifugal separation, the blood cells present in clot 7 pass through the gap between the inner wall 4a of blood collection tube 4 and filter 2 and contaminate serum 6, and the clot becomes attached above filter 2.
An attempt has been made to employ a rubber sheet possessing elasticity in place of the serum filtering piston 1; however, because the resistance of the rubber sheet to sliding is large, it is difficult to move this sheet smoothly down the inner wall of the blood collection tube, and in particular, in the case in which there is a variation in the inner diameter of the blood collection tube such that the diameter becomes smaller toward the bottom of the tube, as is the case in plastic blood collection tubes, it is extremely difficult to move the rubber sheet downwards in a smooth manner, and there is a problem in that it is difficult to completely separate the serum and the clot.
Furthermore, in evacuated blood collection tubes employing rubber stoppers such as those described above, there are problems in that in order to maintain air-tightness, the surface area of the blood collection tube and rubber stopper which are in contact is enlarged, and it is necessary to force this rubber stopper into the tube in a considerably forceful manner, and the rubber stopper itself becomes large, and furthermore, it is not easy to remove the rubber stopper. Furthermore, when a rubber stopper is employed, there is a problem in that it is impossible to prevent the occurrence of the so-called "pop-up" phenomenon. What is meant by the "pop-up" phenomenon is a phenomenon which occurs when the stopper has been removed from the vessel and is then reinserted; as a result of the reinsertion of the stopper, the air within the vessel is compressed, and as a result of the expansion of this compressed air, the stopper comes out.
Furthermore, when an evacuated blood collection tube is employed onto which a gas-barrier-type film is heat-sealed, when centrifugal separation is completed and the serum is to be moved to another vessel, the time-consuming removal of the film must be performed by hand.